Exploring the Stereoselectivity in the Peterson Reaction of Several 2-Substituted 1-Azabicyclo[2.2.2]octan-3-ones

The Peterson reaction between a series of 2-substituted 1-azabicyclo[2.2.2]octan-3-ones and 3-methyl-5-trimethylsilanylmethyl isoxazole (1) was explored. (Z)-Stereoselectivity was obtained with all 2-substituents, ranging from 65:35 for benzyl to 95:5 for phenylsulphanyl. Different bases were investigated, revealing that an organolithium base is necessary for the reaction to occur. A transition state is suggested, involving a four-membered ring in which the lithium ion is covalently bound α to the silyl-group and chelated to the carbonyl oxygen.